1. Field of the Disclosure
The present disclosure relates to a glass manufacturing technique, and more particularly, to a method for forming a lubricant layer on the surface of a glass and a method for manufacturing a glass using the same, which may prevent scratches from occurring at the surface of a glass and decrease corrosion of glass manufacturing equipment.
2. Description of the Related Art
Many kinds of flat glasses are being used in various fields like window panes, window screens of vehicles and mirrors. Such a flat glass may be manufactured in various ways. Among them, a representative method is a production method using a float method. For example, thin glass planes or glass films for TFT displays are frequently manufactured by the float method. The glass manufactured by the float method is called a float glass.
FIG. 1 is a schematic diagram showing a system for manufacturing a float glass.
As shown in FIG. 1, a float glass is generally formed by using a float bath 10 where a molten metal M such as molten tin or molten tin alloy is stored and flows. At this time, a molten glass having a lower viscosity than the molten metal M and lighter than the molten metal M by about ⅔ is successively supplied into the float bath 10 through an inlet of the float bath 10. The molten glass moves to the downstream of the float bath 10 while floating and spreading on the molten metal M. In this process, the molten glass nearly reaches an equivalent thickness according to its surface tension and gravity to form a glass strip or ribbon which is solidified to some extent.
In addition, the molten glass ribbon formed as above is transferred from the float bath 10 to an annealing furnace 20 and experiences an annealing process. In the annealing process, the glass is transferred from an inlet to an outlet of the annealing furnace 20 by transfer means such as a roller 30 or a belt. In addition, after the annealing process, the glass may also be carried by the transfer means such as the roller 30.
While the glass is transferred in the annealing process or after the annealing process, the lower surface of the glass may come into contact with the transfer means such as the roller 30. At this time, due to the transfer means such as the roller 30, flows, cracks or scratches may occur at the lower surface of the glass. Particularly, if the above equipment is used continuously, impurities or glass fractures may be attached to the transfer means such as the roller 30. In this case, scratches may occur more easily at the lower surface of the glass.
If scratches occur at the lower surface of the glass during a glass transferring process using the roller 30 or the lime, the quality and yield of glass greatly deteriorate. Therefore, efforts are being made to prevent scratches from occurring at the lower surface of a glass during the glass transferring process, particularly in the annealing furnace 20, or during a process of transferring a glass after the annealing process.
Among them, a representative technique is to supply SO2 gas to the lower surface of a glass at an initial stage of the glass annealing process or before the glass annealing process. If the SO2 gas is sprayed to the lower surface of a glass as described above, the SO2 gas reacts with alkali components of the glass, particularly sodium components, to form sulphate such as Na2SO4. In addition, the formed sulphate serves as a lubricant layer since its film strength is higher than that of a glass, thereby preventing scratches from occurring at the lower surface of the glass by the transfer means such as the roller 30 and improving the scratch resistance of the glass.
However, in case of a non-alkali glass substantially not containing an alkali component such as sodium, like a glass for LCD, even though SO2 gas is supplied, a sulphate lubricant layer is not easily formed by an alkali metal such as Na2SO4. The SO2 gas should react with components such as alkali earth metal like calcium in the glass to form a sulphate lubricant layer such as CaSO4, but the SO2 gas does not easily react with alkali earth metals or the like in comparison to alkali metals such as sodium. Therefore, in order to form a lubricant layer such as CaSO4, an excessive amount of SO2 gas should be used. However, if a lot of SO2 gas is used, the production cost may increase accordingly. In addition, the toxicity of the SO2 gas may act as a source of environmental pollution and cause serious harm to workers health.
Moreover, since manufacturing equipment or instruments such as the annealing furnace 20 may be easily corroded due to SO2 gas, the productivity and process efficiency when manufacturing glasses may be adversely affected. For this reason, the SO2 gas should be used as little as possible. However, in the conventional technique, an excessive amount of SO2 gas should be inevitably used to form a lubricant layer for preventing scratches from occurring at the lower surface of a glass.